The present invention relates to a device for controlling the rotor rotation of a stepping motor for an electronic watch.
FIGS. 1(a) and 1(b) show a flat plan view and a side view of one embodiment of stepping motor used for analog type electronic wrist watches. In order to rotate a rotor 2 in a predetermined direction by using a drive pulse of alternating polarity, such type stepping motor conventionally uses a magnetic or mechanical index means by which the direction of the rotor rotation is maintained in one direction.
In recent years, however, in the electronic wrist watch, a reversible stepping motor has been required in order that many functions, such as, time correction or correction of the difference in time, can be achieved electrically.
In the prior art, some reversing drive techniques have been proposed, such as, a technique for moving the direction of the index mechanically, or a technique which comprises detecting the position of the rotor by using a current waveform or the like, and selectively adding a pulse which changes its polarity at the precise time to obtain reverse drive. However, these techniques are not suitable for mass-production of electronic timepieces. Furthermore, it is difficult to achieve high-reliability rotor reversal without a decrease in performance at the time of rotor rotation.
The basic object of the present invention is to provide a device for controlling the rotor rotation of a stepping motor for an electric watch and which can be driven by a single coil.